Oil spills due to releases of crude oil from tankers, offshore platforms, drilling rigs, and wells, as well as spills of refined petroleum (such as gasoline or diesel) and their by-products, and heavier fuels used by large ships such as bunker fuel, if uncontrolled may have devastating and lasting environmental impact. Such spills may be controlled by chemical dispersion, combustion, mechanical containment, and/or adsorption. Controlled burning can reduce the amount of oil in water, but can only be done in low wind conditions. Dispersants create smaller oil droplets which may be scattered by currents, and may degrade more easily. Dry hydrophobic, water insoluble polymers that both adsorb and absorb hydrocarbons can clean up oil spills by changing the physical state of oil from liquid to a semi-solid or a rubber-like material that floats on water, rendering it readily collectable. However, collected solidifiers must be disposed of in landfills, recycled as an additive in asphalt or rubber products, or burned as a low ash fuel. Oil-absorbing materials such as hair and fabrics may also be used. Oil may be “vacuumed” from the surface, along with some water, and the mixture centrifuged to separate the oil from the water, thereby permitting nearly pure oil to be collected, the water often being returned to the sea. Oil skimming devices may also be used.
Typically, large floating barriers, known as booms, are used to surround and confine an oil slick, thereby enabling chemical and biological agents to be added to the oil to encourage its breakdown, and mechanical techniques to be used more efficiently.
The ever-growing importance of Arctic waters as sources of oil and natural gas generates additional challenges for spill responses. As stated above, examples of responses for mitigating adverse effects of oil spills include the use of dispersants, in-situ burning, and mechanical recovery, with mechanical containment and recovery being the most preferable. However, use of conventional booms and skimmers for mitigation of oil spills is challenging in seawater where ice is present.
Surfactants presently used for contracting oil slicks include mixtures of Span®, a water insoluble surfactant, and 2-ethyl butanol, an organic co-solvent. The U.S. Navy formulations for such uses include: (a) 75% Span® 80 and 25% of an organic co-solvent for warm water applications; (b) 65% Span® 20 and 35% of an organic co-solvent for cold water applications; and (c) 35% Span® 20 and 65% of an organic co-solvent for “winter” blend applications. The organic co-solvent is important when liquid forms of surfactant or surfactant mixtures are desirable. Thickslick 6535 has recently been offered by a contractor of ExxonMobil for contracting oil slicks for subsequent in situ burning. The 2-ethyl butanol co-solvent is toxic and biological degradation is very slow.
Proposed surfactant materials and formulations include mixtures of non-ionic surfactants and anionic surfactants, for example Corexit 9527, fluorine-based surfactants, and silicone-based surfactants, such as Siltech OP-40.